refactor 'dir = ' into 'set_dir()'

This should have little/no gameplay effect right now, just paving the
 way for directional lights.
Replaced handle_rotation() on buckly things with this.

Signed-off-by: Mloc-Argent <colmohici@gmail.com>
Merge pull request #7205 from Mloc/bs12-setdir

refactor 'dir = ' into 'set_dir()'